Trastuzumab deruxtecan (T-DXd) versus trastuzumab emtansine (T-DM1) in patients (pts) with HER2-positive (HER2+) unresectable and/or metastatic breast cancer (mBC): Safety follow-up of the randomized, phase 3 study DESTINY-Breast03.
Authors: Erika P. Hamilton, Vanessa PETRY HELENA Bragaia, Winnie Yeo, Sung-Bae Kim, Giampaolo Bianchini, Toshinari Yamashita, Kan Yonemori, Kenichi Inoue, Giuseppe Curigliano, Sara A. Hurvitz, Javier Cortes, Hiroji Iwata, Jillian Cathcart, Yali Liu, Caleb C. Lee, Emarjola Bako, Rachel Kim, Seock-Ah Im
Journal: Journal of Clinical Oncology (2022)

1000 Background: In the DESTINY-Breast03 (NCT03529110) primary analysis (data cutoff [DCO], May 21, 2021), T-DXd showed superiority over T-DM1 in pts with HER2+ mBC, with a significant improvement of progression-free survival by blinded independent central review (HR, 0.284; 95% CI, 0.217-0.373; P &lt; 0.001), and a safety profile consistent with prior studies. This analysis provides updated safety data with longer follow-up. Methods: Pts were randomized 1:1 to T-DXd or T-DM1. Prespecified safety analysis of treatment-emergent adverse events (TEAEs) was conducted; endpoints included time to event, duration of event, and resolution. Results: At DCO (September 7, 2021), 116 (45.1%) pts vs 39 (14.9%) pts remained on treatment in the T-DXd vs T-DM1 arms; median treatment duration was 16.1 mo (range, 0.7-33.0) for T-DXd vs 6.9 mo (range, 0.7-28.5) for T-DM1. Any-grade (G), G≥3, and serious AE (SAE) rates were similar for T-DXd vs T-DM1 (99.6% vs 95.4%; 53.3% vs 49.8%; and 21.0% vs 19.2%), while exposure-adjusted incidence rates (EAIRs; per pt-year) for G≥3 and SAEs were lower for T-DXd vs T-DM1 (0.42 vs 0.70 and 0.17 vs 0.27). Median time to TEAE associated with drug discontinuation or dose reduction was longer with T-DXd vs T-DM1 (224.0 vs 147.0 d and 96.0 v 19.0 d, respectively). Most TEAEs in ≥20% of pts were hematologic or gastrointestinal. Median time to first onset of select any-G TEAEs was 70.0 vs 42.0 d for anemia, 196.0 vs 168.0 d for lymphopenia, 132.0 vs 8.0 d for thrombocytopenia, 22.0 vs 24.0 d for fatigue, 74.5 vs 92.0 d for leukopenia, and 64.0 vs 105.0 d for neutropenia, with T-DXd vs T-DM1, respectively. In both arms, most nausea and vomiting events were G1/2; while G≥3 events with T-DXd vs T-DM1 were 6.6% vs 0.4% for nausea and 1.6% vs 0.8% for vomiting, respectively. Rates of nausea, vomiting, and alopecia were highest in cycle 1 and lower in subsequent cycles for T-DXd. Rates of hematologic events were generally lower in earlier cycles vs cycle ≥8 in both arms. Rates of adjudicated, drug-related ILD/pneumonitis were 10.9% (1 G2 event since previous DCO) with T-DXd vs 1.9% with T-DM1, with no G4/5 events. Median time to first adjudicated, drug-related ILD/pneumonitis event was 5.9 vs 9.5 mo for T-DXd vs T-DM1, respectively; at DCO, most events resolved (57.1% vs 80.0%), and follow-up is ongoing. Conclusions: In this updated safety analysis, T-DXd demonstrated a tolerable safety profile consistent with prior studies. Despite longer treatment duration with T-DXd, EAIRs of G≥3 and SAEs were lower for T-DXd vs T-DM1. Rates of ILD/pneumonitis for T-DXd were similar to those in the previous DCO. Nausea, vomiting, and alopecia rates decreased over time. This longer safety update reinforces the consistent safety profile of T-DXd, supporting the clinical benefit of T-DXd over T-DM1 in patients with HER2+ mBC. Clinical trial information: NCT03529110.